Spring means for roller mills and the like



July l, 1952 J. cRlTEs 2,601,954

SPRING MEANS FoR ROLLER MILLS AND THR LIRE Filed Nov. 17, 1949 2 SHEETS-SHEET 1 classifier Q Spring Compression, lbs.

July l 1952 J. cRrrl-:s

SPRING MEANS FoR ROLLER Mms AND THE LIRE Filed Nov. 17, 1949 2 SHEETS-SHEET 2 INVENTOR Joe Cmes "Y @5i TTo EY um ,......|L w mw nu IH Patented July 1, 1952 SPRING MEANS` Fort ROLLER lvriLLs ND THE uns .loe Crites, Larchmont, N. Y., assigner to Combos; tion Engineering-Superheater, Inc., New York, N. Y., a corporation of Delaware Application November 17, 1949, Serial No.7127,19$0

(Cl. 24k-133) 3 Claims. l

This invention relates to roller mills and the like, and particularly to improved means for maintaining desirable pressures upon the material being ground between the rolls and the grinding member (ring, bowl, table or the like) in such mills.

Heretofore, in mills of the so called roller type here considered, the pressure on the material has been produced by means employing a single spring acting to force each roll against the grinding member, the pressure being varied by varying the compression of the spring.

Preferred spring means should provide the proper pressure on each material of a different grindability being ground under the roll and at a suitable predetermined gap between the roll and the grinding member (illustratively referred to hereinafter as ring or bowl). However said pressure should not become excessive when the gap is materially increased by the passage therethrough of foreign matter, such as tramp iron. Furthermore said spring means should preferably provide a relatively low pressure on the roll when the roll is near the ring because then the roll will nip material, such as coal, with a rolling action instead of tending to plow it aside as is the case when the pressure is higher. Also the pressure on the roll should be low when the roll is near the ring to minimize noise and vibration; for with high Vspring pressure and Va small gap. between the roll and ring, there is no thick cushion of material kto absorbthe noise or vibration. But it is desirable to have the pressure build up rapidly as the material in the bowl accumulates to get quick response to changesin output; for example when the mill is used for firing steam boilers in power plants.

Heretofore the above mentioned preferred advantages have not been realized in roller mills when the pressures on the rolls were produced by means employing a single spring, and it is an object of this Ainvention to provide yimproved. spring means, in mills employing grinding rolls, for regulating the pressures of said rolls against the material be'ngfground in a manner to achieve said advantages.

Other objects and advantages of my invention will become apparent from the following description of an illustrative embodiment thereof when taken in conjunction with the accompanying drawings, wherein;

Fig. 1 is an elevation of a bowl-type of roller mill with` a portion of the casing broken away to show interiorly a typical roll and exteriorly that rolls associate-d improved spring means ernbodying the invention;

2 Figs. 2 and 3 are respectively side and front elevations of the improved spring means; and Fig. 4 is chart showing the resultant spring pressures acting on the roller for various spring compressions, when employing the invention.

Referring to Fig. l., the roller mill, here shown by way of example as of the well known Bowl ivre, comprises a has@ l SurpQrigng .a .Casing 2-2 there-abovewithin the lower portion 2 of which is a bowl 3 mounted for rotation about a vertical Shaft i The Shaft i isurrorted in bearings (not Shown) @Quilted Within the base l and iS rotated bya system of bevel gears (also not shown) within the base I. Said gearsare in turn driven by a motore through shaft E,

The bowl 3 Contains a Peripheral grinding ring 'I onto which the material to be ground flows by centrifugal force from the inner portion of the rotating bowl. The material to be ground is Supplied to the bowl downwardly from the mill top through a central feed tube 8 from which it passes further downwardly from the upper casing portion 2 through opening Sinto the lower casing portion 2. t The rotation of thebowl carries the material flowing onto the ring 'I to the rolls 9 where it is ground inpassing between the rolls 9 and the ring 1.

An air current flows in well `known manner upwardly between the rim of bowl 3 and the surrounding casing 2 and carries .the sufficiently ground material up through the mill, as shown by the arrows, and out through the top off-take K; The vinsuiiiciently ground material is separated out of the vair stream by the represented classifier Q and falls back into the bowl through opening' to be further ground.

The particular bowl mill here shown is equipped with three rolls 9 (only two can Vbe seen in Fig. 1) Each roll S is mounted to freely rotate about thelower end of a shaft i0 which shaft is fastened at its upper end to an arm` l I. Arm Il is mounted to' freely rotate on trunnions l2 which are carried in bearings I3, one of which is shown in cross section, mounted onthe cover Hl of casing 2L Arm Ilv extends radiallyoutwardly of the mill and terminates in a head ll'beyond the outer edge of cover It, against the bottom of which head |5'the upper end of the main pressure spring lil bears.

As shown in detail in Figs. 2 and 3, the means for supporting the main pressure spring I6 comprises the members Il extending radially from the cover iii on either side of the spring, each of which is slotted to receive one of the` two vertical bolts i8 which are fully threaded Vand fastened tothe members IIvby top and bottom nuts I9. A

yoke 20 straddles the bolts I8 at their lower ends,

is supported by nuts 25 on said bolts, and formsV a spring seat 2I against which the lower end of the main pressure spring I6 bears.

Fastened to the bolts I8 above the members I1 by nuts 22, is a cross bar or stop 23 which serves to stop the upward movement of the head I of arm I I. A round rod 24 (see Figs. 2-3) is fastened to the top side of head I5 to form the contact with cross bar 23. If the main spring I 6 is compressed, then by raising or lowering the cross bar 23 along bolts I8 by adjustment of nuts 22, the arm head I5 will be raised or lowered and the roll 9 will respectively be brought nearer to or farther from the grinding ring 1.

In this manner the gap between roller 9 and ring 1 may be varied. By raising or lowering the bottom yoke 20 along bolts I6 through adjustment of nuts 25, the compression of the main spring I6 may be increased or decreased and therewith the pressure against the head I5 of arm I Iand consequently the pressure on the material being ground between the roll 9 and the grinding ring 1.

The control of the gap between roll 9 and ring 1 and the pressure exerted by the main spring I6 on the material passing therethrough as described above, has heretofore been in common use.

According to this invention I provide a relief spring 26 which is seated at its upper end in a yoke 21 fastened to bolts I 8 by nuts 26. The lower end of the relief spring 2'6 seats on a member 29 having plunger 30 which passes freely through a bore in the cross bar 23 and rests on the rod 24 of the head I5 of arm II. A shoulder 3| on member 29, at the upper end of plunger 30, serves as a stop for its downward movement when it strikes the top of the cross bar 23.

By varying the gap 32 between the shoulder 3l and the cross bar 23, as by the insertion of shims 34, the movement of relief spring 26 may be limited. The compression relief spring 26 may be varied by the adjustment of the nuts 28 of yoke 21 along the bolts I8.

In operation, instead of depending upon the compression of main Spring I6 alone for exerting the pressure on the roll 9, as was done heretofore, I now can controllably lower said pressure for a predetermined movement of the upper end of spring I6 by the opposing action of the relief spring 26 on the head I5 of arm II. The new and advantageous results in mill performance which are attained by said combined action of the main and relief springs are discussed below.

Referring to Fig. 4, A represents the initial compression of the main spring I6 along line OA, and a that of the relief spring 26 along line Oa. The resultant pressure against the head I5 of arm I I is A-a, which is also the pressure against the cross bar 23 when there is no material passing under the roll 9. The roll 9 is usually spaced from the grinding ring 1 so that in the absence of material therebetween, the cross bar 23 receives this resultant pressure of the springs.

When material is being ground between roll 9 and ring 1, the roll will depart further from the ring so that main spring I6 may be compressed to B or to C or to D or to E while the relief spring 26 will expand respectively to b or to c or to d or to O. The respective resultant pressures against head I5 of arm II' are B-b or C--c or D-d or E; and in Fig. 4 these are plotted in line with the corresponding positions A, B, C, D, E of the upper fil) end of main spring I6, which also represent the downward movements of head I5 of arm II.

The Resulta-nt line has a much flatter slope than the line AE representing the main spring and therefore the combined spring action provides greater pressure variations than the single main spring used heretofore, for the same movement.

These greater pressure variations are of especial advantage when grinding diiferent grades of coals. For low grindability coals a relatively high roll pressure is desirable while for high grindability coals about half of said pressure is desirable with a closer gap between roll and ring. These conditions are satisfactorily met by the combined springs I5 and 26 as uniquely organized by me, but not by the single spring I6 used heretofore. The new arrangement will then permit grinding various grades of coals without adjusting spring pressures.

Furthermore, it is desirable to have the pressure build up rapidly as the material in the mill bowl 3 accumulates so as to get quick response to changes in load, for example, when the mill is used for firing steam boilers in power plants; and my new double spring arrangement effectively provides for this.

Also because of the lower spring pressures when the roll 9 is near the ring 1, it will nip the coal with a rolling action instead of tending to plow it aside as is the case when the pressures are higher.

Another advantage of these lower spring pressures lies in a quieter running mill over a wide range of capacities. With a light pressure on the roll 9, there is a minimum of noise and vibration when that roll is near the grinding ring 1; and this is of especial advantage since under the conditions stated there is no thick cushion of material to absorb noise or vibration.

Although the combined springs I6 and 26 provide the advantage of greater pressure variations for the same movement than are obtained by the single main spring I6 as used heretofore, it would be possible to substitute a single, much heavier spring which would compress along the Resultant line of Fig. 4. However the use of such a heavy spring becomes objectionable when the gap between the roll and ring is materially increased by the passage therethrough of foreign matter, such as tramp iron. The resulting high compression of such a heavy spring would then cause a prohibitive pressure on the roll and arm I I. But when using the opposing springs, according to my invention, the gap 32 between the shoulder 3| of member 29, and the cross bar 23 may be limited so that beyond the normal movement of the head I5 of arm II, shoulder 3l will seat on cross bar 23 and limit the action of relief spring 26. Thereafter the main spring I6 alone will act upon head I5 of arm II and the rate of pressure increase will be reduced.

Referring to Fig. 4, if the gap 32 is set to close at B-b, or at C-c, or at D-d, the pressures will rise from there to B, or to C, or to D respectively (along the dashed lines), and thence increase along line AE representing the compression of the main spring. Obviously many variations in choice of springs and in their opposing pressures may be made.

While I have here disclosed my invention as being applied to a bowl-type mill having rolls 9 urged towards a grinding ring 1 carried by a rotatable bowl 3, it will be apparent that such disclosure is illustrative rather than restrictive and that my inventive improvements may with, ,n

comparable benefit also be applied to mills of other types, such as those using rollers'or balls running adjacent tables or races, wherein the problem solved by this invention is encountered.

Moreover, even though only one illustrative embodiment has been shown and described, it will be understood that changes in construction, combination and arrangement of parts may be made Without departing from the spirit and scope of the invention as claimed.

I claim:

1. In a roller mill having a casing and a rotating bowl therein including a grinding ring, a roll mounted in the casing arranged to roll on and grind material between the roll and ring, shaft means on which said roll is mounted for rotation thereon, a trunnion bearing mounting said shaft means on said casing about which trunnion said roll may be moved toward and away from said ring, a main spring arranged to act at its one end on a portion of said shaft means to urge said roll toward said ring, a stop bar engaging said portion to limit the movement of said shaft means and therewith the movementY of said roll toward said ring, at least one bolt mounted on said casing and nuts on said bolt adjustably supporting' said stop bar longitudinally of said bolt, a relief spring arranged to act at its one end on said portion of said shaft means to oppose said main spring and tending to urge said roll away from said ring, a member interposed between said relief spring and said portion of said shaft means having a plunger, means forming a bore in said stop bar through which said plunger freely moves to act on said portion, adjustable means mounted on said stop bar engaging said member to limit the action of said relief spring, and a crossbar adjustably supported by nuts longitudinally of said bolt and bearing against the other ends of each of said main and relief springs to individually vary the pressure exerted by either of said springs on said portion and said roll and thereby on said material.

2. In a roller mill having a casing and a rotating bowl therein provided with a grinding surface, a roll mounted in the casing arranged to roll on and grind material betweenthe roll and grinding surface, a shaft adjacent one end of which said roll is mounted for rotation thereon, an arm extending from said shaft adjacent the other end thereof and fastened thereto, a pin on said arm adjacent said shaft journaled on said casing to rotate said arm and therewith said shaft and roll to move said roll toward and away from said grinding surface, a head on said arm at its extended end for receiving one end of a main spring, said main spring acting to urge said roll toward said grinding surf-ace,'means for `adjusting said spring to vary the pressure against said head, a stop bar mounted on the easing to limit the movement of said head and therewith the movement of said roll toward said grinding surface, means adjusting the position of y said stop bar with respect to said arm head and therewith the gap between said roll and said grinding surface, a relief spring acting onV said arm head in direction opposite to said main spring, means for adjusting said spring to vary the pressure against said head, and means on said bar to adjustably limit the action of said relief spring.

3. In a roller` mill having a casing and a rotating bowl therein including a grinding ring, a roll mounted in the casing arranged to roll on Iand grind material between the roll and ring, a shaft adjacent one end of which said roll is mounted for rotation thereon, an arm extending from said shaft adjacent the other end thereof and fastened thereto, a pin on said arm adjacent said shaft journaled onV said casing to rotate said arm and therewith said shaft and roll to move said roll toward and away from said ring, a head on said arm' at its extended end for receiving one end of a main spring, ,said main spring acting at one end to urge said roll toward said ring, a bar engaging said head to limit the movement thereof and therewith the movement of said roll toward said ring, bolts mounted on said casing and nuts on said bolts adjustably supporting said stop bar longitudinally of said bolts, a relief spring acting at one end on said arm head in direction opposite to said main spring, a member having a plunger interposed between said relief spring and said arm head, means forming a bore in said stop bar through which said plunger freely moves to act on said arm head, shims mounted on said stop bar engaging said member to variably limit the action of said relief spring, and a crossbar adjustably supported by nuts longitudinally of said bolts and bearing against the other ends of each of said main and relief springs to individually vary the pressure exerted by either of said springs on said arm head and said roll and thereby on said material.

JOE CRITES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 964,224 Emerick July 12, 1910 1,806,980 Kreutzberg May 26, 1931 1,943,142 Peters Jan. 9, 1934 2,079,155 Crites May 4, 1937 2,192,310 Hartshorn Mar. 5, 1940 2,342,255 Doyle Feb. 22, 1944 2.431.746 Frangquist Dec. 2, 1947 

